Conventional pillows are usually filled with a cushioning filler material of cotton wadding or batting, feathers, down, sponge rubber, fiber fill or foam. Among these materials, down shows excellent properties in bulkiness, softness, thermal insulation, compression recovery and moisture transmission. Many people, however, are allergic to down, and down may harbor not only allergens, but also insects and bacteria. Down is also cost prohibitive for many applications.
Cotton, compared with down, has inferior bulkiness, softness and thermal insulation. Its compression recovery is not as good as down or some of the synthetic filling materials. When damp, the cotton wads together and does not sufficiently recover to its uncompressed state.
The synthetic materials have advantages over the natural materials, in view of cost, durability and health concerns. Polyester fiber fill is an especially popular filling material. Other synthetic fibers used as fillers include polyethylene, polypropylene, polyamide and aramides. A matrix of straight fibers is pre-fluffed with a picker apparatus to separate the fibers to permit their insertion into a cushion or pillow casing. The fibers are then blown through an injector or plurality of injectors into cavities formed in the casing. With cushion use, fibers tend to bunch up and create pockets which permit the cushion or pillow to "bottom out". Particularly, it has been found that fibers nest and clump together when blown into larger volume casings or casings with complicated shapes. Thus, in an effort to prevent undue clumping of fibers, larger or more complicated cushions are separated by ticking into several smaller compartments that are filled with the fibers.
To eliminate some of the crushing and clumping associated with straight fiber filling materials, U.S. Pat. No. 3,922,756 proposes forming the fibers into a filamentary spherical body. Spherically intertwined fiber aggregates also are shown in U.S. Pat. Nos. 4,998,309 and 4,794,038.
In lieu of fiber fill, blocks of sponge rubber or foam may be shredded into chunks or particles that are used as filling materials for cushions and pillows. The edges of the shredded foam chunks tend to hook together, which creates regions with more foam and regions with less foam within the cushion core. The foam chunks or particles do not reproduce the cushioning plushness of fiber fill or down.
To address the clumping problems associated with fibers, U.S. Pat. No. 5,061,737 suggests combining fiber fill (1-3 inch long fibers) with shredded polyurethane foam chips (1/4 inch blocks) to form a filling material. The fibers are coated or slickened with a silicone finish prior to mixing with the shredded foam. The patent states that the length and diameter of the fibers relative to the size of the foam chips and the limited movement permitted by the slickened fiber surfaces affords adequate cushioning support while still maintaining the cushion shape.
U.S. Pat. No. 4,109,332 proposes using polyurethane foam cut into polygonal shaped rods. The rods have flat planar top, bottom and side surfaces, and preferably have a length and width proportionally greater than the rod thickness (or height). The patent emphasizes the importance of the planar nature of the side areas to prevent the rods from hooking on to one another when used as a filling for cushions.
Other synthetic filling materials include engineered elastomeric spheres, U.S. Pat. Nos. 4,754,511 and 5,608,936, pebbles or beads, U.S. Pat. Nos. 3,608,961 and 3,999,801, or tubular hollow forms.
To date, the prior art has not shown cellular polymer or flexible foam filling materials that can be readily inserted by blowing or other means into the chambers of cushion, upholstery cushion and pillow casings without the need for additional ticking or compartments, that repeatedly recover from compression, that avoid clumping and nesting thereby preventing pockets and "bottoming out", and that may be made economically as compared to prior filling materials.